Field of the Invention
This invention generally relates to endoscopes and particularly to maximizing illumination provided by stereoscopic or other endoscopes that contain multiple optical channels.
Description of Related Art
FIG. 1 is cross section of a single-channel endoscope 10 constructed in accordance with known traditional methods. In this specific embodiment the endoscope 10 includes an inner tube 11 that contains a single lens train (not shown) to form an optical train subassembly. An outer tube 12 is concentric with the inner tube 11 and forms an annulus which contains optical fiber 13. With this construction the optical fiber 13 fills the annulus, is sandwiched between the inner and outer tubes 11 and 12 and is constrained along the entire working length of the endoscope 10. As the annulus is filled, its entire volume is used to transfer illumination from an external source to an object being viewed at the distal end of the endoscope.
FIG. 2 depicts a cross-section of a stereoscopic endoscope 20 also constructed in accordance with known, traditional methods. In this embodiment, the endoscope 20 includes an outer tube 21 that carries an optical lens train subassembly 22 within an inner tube 22A and another optical lens train 23 within an inner tube 23A. Two optical fiber bundles 24 and 25 are positioned between the outer tube 21 and the optical train subassemblies 22 and 23, and each is enclosed in a sheath 26. This construction allows the optical train subassemblies 22 and 23 to be mounted without interference with the optical fiber bundles 24 and 25. However, the requirement for fitting the optical fiber bundles 24 and 25 between the outer tube 21 and the optical train subassemblies 22 and 23 limits them to a construction that leaves unused voids 28 along the length of the endoscope 20.
As known, when the illumination at the distal end of an endoscope increases, it is easier to obtain a high quality image. That is, for a given optical design image quality is dependent upon the level of illumination at the object being imaged beyond the distal end of the endoscope. As the construction in FIG. 2 does not fill the voids 28 between the outer tube 21 and the optical train assemblies 22 and 23, the illumination level at the object is less than a maximum value. Consequently, in many instances, particularly as stereoscopic endoscopes are made with smaller outside diameters, image quality suffers. Yet such a construction has remained the construction of choice for stereoscopic endoscopes.